1. Field of the Invention
The present invention relates to an automatic transmission for an internal combustion engine-transmission integral type power unit mounted on a four-wheel buggy car (saddle-ride type vehicle for operating on irregular surfaces) or the like.
2. Description of Background Art
Japanese Patent Publication No. Sho 57-2953 discloses a conventional crankshaft of an internal combustion engine and a main shaft of a transmission that are disposed on one straight line. Power is transmitted in a series manner from the crankshaft of the internal combustion engine to a torque converter disposed at an end of the main shaft of the transmission. In addition, oil hydraulic clutches are disposed, respectively, on the main shaft and a counter shaft.
Conventionally, the crankshaft of the internal combustion engine and the main shaft of the transmission have been disposed in series on one straight line, so that the overall length of the power unit is large. This structure is unsuitable for mounting on a four-wheel buggy car or a motorcycle. When the crankshaft and the shaft of the transmission are disposed in parallel to each other in a conventional constitution, for the purpose of obviating the above-mentioned inconvenience and shortening the overall length, the outside diameters of the crankshaft and the clutches will interfere with each other. Therefore, the spacing between the shafts must be enlarged. This approach has a problem in that the power unit becomes large in size and the weight is also increased.
The present invention solves the above-mentioned problems. The present invention is directed to an automatic transmission including a main shaft and a counter shaft which are disposed parallel to a crankshaft. The rotation of a torque converter is provided on the crankshaft being transmitted to the main shaft through bearings. A two-stage speed change is conducted by gears provided on the main shaft and the counter shaft. An oil hydraulic clutch is provided for connection and disconnection between these gears. A tubular auxiliary main shaft is rotatable relative to the main shaft and is provided at the outer circumference of the main shaft. A first-speed drive gear and a rearward-running drive gear are fixed on the auxiliary main shaft. A first oil hydraulic clutch for enabling contact and separation between the main shaft and the auxiliary main shaft is disposed on the outside of one of a pair of support portions for supporting the main shaft. A second oil hydraulic clutch for enabling contact and separation between a second-speed drive gear which is in loose fit on the main shaft and engaged with a second-speed driven gear fixed on the counter shaft and the main shaft is disposed on the outside of the other of the pair of supporting portions for supporting the main shaft.
According to the present invention, the crankshaft and the main shaft are thus parallel to each other, so that the overall length of the power unit can be shortened. In addition, since the oil hydraulic clutches are disposed at end portions on the outside of the front and rear support portions for the main shaft, it is possible to obviate interference among the torque converter, a crank, an AC generator and the like on the crankshaft.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.